1. Field of the Invention
The present invention relates to a transfer belt unit and an image forming apparatus. More particularly, the present invention relates to a transfer belt unit in which meandering of a transfer belt for transferring a toner image onto a printable medium is substantially prevented, and an image forming apparatus having the same.
2. Description of the Related Art
Examples of printable mediums include paper sheets on which an image is to be printed, photographic paper, overhead projector (OHP) film, and so forth. Examples of image forming apparatuses include printers, scanners, copying machines, facsimiles, and multi-functional peripheral (MFP) devices in which two or more devices are converged.
Electrophotographic image forming apparatuses form an electrostatic latent image that matches with printing data by irradiating light onto a photosensitive medium. The electrostatic latent image is developed with a toner image using a developing unit. The toner image is transferred onto a printable medium using a transfer belt unit. The toner image is fused on the printable medium using a fusing unit, thereby printing printing data inputted from an external computer on the printable medium.
The transfer belt unit includes a transfer belt and a plurality of rollers that support and drive the transfer belt. The transfer belt directly transfers the toner image onto the printable medium by traveling while the printable medium contacts an outer circumference of the transfer belt, or performs secondary transferring onto the printable medium after the toner image is first transferred on the outer circumference of the transfer belt. Thus, the transfer belt should travel in a straight direction that is identical to a feeding direction of the printable medium so that precise printing can be performed.
However, when a thickness difference exists in the transfer belt, a difference in length occurs in both ends of the transfer belt in a traveling direction such that rotating axes of rollers are not parallel to each other or an outer diameter difference exists in rollers that contact the inner circumference of the transfer belt. This results in the traveling direction of the transfer belt not following a straight line and cause the transfer belt to meander.
When the transfer belt meanders, the toner image of the transfer belt deviates. Particularly, when a color printing operation is performed, superpositioning of respective color images fails so that precision of color registration is lowered. Thus, a unit for substantially preventing meandering of the transfer belt is required. The unit for substantially preventing meandering of the transfer belt guides the transfer belt along a straight line in the traveling direction and substantially prevents a difference in a traveling speed. When the difference of a traveling speed occurs in a partial position at a specific time so that the traveling speed of the transfer belt is not uniform, transfer quality may be degraded at the point of time or in the position intermittently.
Accordingly, a need exists for an image forming apparatus having an improved transfer belt unit that is substantially prevented from meandering and is maintained at a substantially uniform traveling speed.